/Engine/Plugins/Media/PixelStreaming/Source/PixelStreaming/Public/PixelStreamingSessionDescriptionObservers.h
Errors usually mean incompatibility between our session configuration (often H.264, its profile and level) and player, malformed SDP or if player doesn't support UnifiedPlan (whatever was used by proxy)
void OnFailure ( webrtc::RTCError Error )